1. Field of the Invention
The present invention relates to control device and a control method for a vehicle equipped with an automatic transmission. More specifically, the present invention relates to a vehicle control for switching a shift lever position selected by the driver from a neutral position to a forward drive position.
2. Description of the Related Art
In a vehicle equipped with an automatic transmission, the driver may move the shift lever in order to change shift lever position from a neutral position (referred to as an “N position” below) to a forward drive position (referred to as a “D position” below), which will be referred to as an “N/D operation” below. Friction engagement elements that were released are consequently engaged such that the automatic transmission switches from neutral to the D-range. Significant shift shock may be generated if the driver depresses the accelerator pedal immediately after performing an N/D operation. Art for suppressing such shift shock is described in Japanese Patent Application Publication No. JP-A-61-105228, for example.
The control device for an automatic transmission described in JP-A-61-105228 includes: a shift operation sensor that detects an operation to shift from a stop range to a running range; a vehicle speed sensor that detects a vehicle speed; an engine speed sensor that detects an engine speed; and an output torque reduction unit that reduces the engine output torque alongside a transition to engaging a running-range friction engagement device when there is an operation to shift from the stop range to the running range while the vehicle speed is equal to or less than a predetermined vehicle speed, and when the engine speed becomes equal to or greater than a predetermined engine speed within a predetermined time since the shift operation.
According to the control device for an automatic transmission described in JP-A-61-105228, if the driver attempts to perform a shift operation and immediately start moving the vehicle (that is, when there is an operation to shift from the stop range to the running range while the vehicle speed is equal to or less than a predetermined vehicle speed, and the engine speed becomes equal to or greater than a predetermined engine speed within a predetermined time since the shift operation) the engine output torque is reduced when engaging the D-range friction engagement device. Therefore, the torque borne by the D-range friction engagement device upon engagement thereof is kept within a tolerance value and sudden fluctuations in the output shaft torque of the automatic transmission upon engagement of the D-range friction engagement device are suppressed. The shift shock and shock load can thus be alleviated. There is also no need to delay the engagement of the running-range friction engagement device, so a delay in starting vehicle travel may be avoided.
However, if the above N/D operation is performed while the vehicle is in motion, it may be necessary to engage two friction engagement elements in order to form a gear higher than the forward first gear. If the accelerator pedal is depressed immediately after performing the N/D operation, leads to the engagement of the friction engagement elements, as well as an increase in the torque input to the friction engagement elements. Accordingly, the hydraulic pressure to the friction engagement elements must also be increased in order to prevent slipping of the friction engagement elements. This may consequently generate engagement shock due to the imbalance between the engagement state of one friction engagement element and the engagement state of the other friction engagement element.
In order to appropriately suppress such engagement shock, until the friction engagement elements are completely engaged, the output torque of a drive source (an input torque of the automatic transmission) may be decreased considerably more than when only one friction engagement element is engaged. However, this means that the vehicle does not accelerate even though the accelerator is being depressed, and gives the driver a sense of incongruity.
JP-A-61-105228 and Japanese Patent Application Publication No. JP-A-2003-287122 do not provide any solution to the above problem.